There is a sheet post-processing apparatus that performs post-processing for applying post-processing such as sorting and stapling to a plurality of sheets conveyed from an image forming apparatus. The sheet post-processing apparatus includes a standby tray for putting the sheets on standby and a processing tray for applying the post-processing to the sheets. However, in the standby tray, a jam is likely to be caused by a collision of the sheets put on standby and the sheets conveyed to the standby tray.